Roasting and/or sintering of fine ores or other fine materials



' Jan. 20, 1931. A. D. H. 1.. FASSOTTE I 1,789-895 ROASTING AND/OR SINTERING OF FINE ORES OR OTHER FINE MATERIALS Filed Nov. 17, .1927

,a pawn man, 1931 UNITED STATES PATIENT OFFICE anorrnn name mar mon ruse-rm, or noirnlnQrnmm aoisrme mm; srarnanm or rnra ones on or'm a rnm mraams Application fled November 17, 1927, Serial No. 283,982, am1 in Belgium January 88,

This invention relates to the roasting and/or sintering of fine ores or other fine materials, more particularly of zinc ores.

It is known in processes for the roasting or sintering of sulphurous, or arsenical, orother ores, capable of reacting with air, with or without the addition of fuel, to sub'ect the said ores on a grate to the action drawn or blown blast. For this purpose, the contents of the ore in a heat generating element (5, As, or other) is reduced to such an extent t at the temperature which is necessary for a rapid and total reaction shallbe reached, without the fusin point of the ore being reached, thus keeping the reaction from suppressing the assage of the air. This result is generally 0 tained by a preliminary roasting, or by the mixing of materials already roasted with unroasted material.-

fine ore pervious to the air by adding water and a binding material such as clay or like material, or a combustible substance such as coal.

In all these processes, onl a relative and irregular permeability of't e layer ofmaterial is obtained, which implies:

The necessity-of working with a ve thin layer, resulting in a small output of t e apparatus;v

The necessity of blowing ordrawing in air at a high pressure thus a high consumption of motive power. and, owing to thefin'eness of the material, a strong tendency to the forma- 86 'tion of holes and considerable losses of ore in the form of fine dust;

The formation of too hot andtoo cold regions, due to the difference ofpermeability, which involves either the volatilization of valuable metalsor the production of an imperfectly roasted or sinteredsubstance.

It is also known in a process of making agglomerates from fine ore, to mix the fine ore with fine fuel and to add to the mixture 30 to of water to form an easily kneadable pulpous mass, which is then conveyed to an extrusion press (brick making press) adapted to form pieces of any suitable size These pieces are then charged into a shaft These known processes seek to render the furnace where they are heated to a sintering temperature.

In this process, the use furnace implies the necessity of charging therein agglomerates of comparatively large e size and 0 very high resistance to allow t air to pass through the column of material piled in the furnace and to prevent the crushing of the agglomerates by their own wei ht. This large size for the agglomerates and t eir great compactness, as well as the larger .dimensions of the interstices make it impossible to obtain a complete-roasting or uniform sintering of the ore.

The present invention contemplates a roc-. ess for the roasting and/0r sintering o fine ore or other fine material consisting essentially in subjectin the ore to a preparation adapted to reduce t e ore to small sized grains which are afterwards subjected in .a uniformly and highly 'pervious thin layer to a roasting and/or sintering operation on the ofa shaft or highgrate of av suitable apparatus traversed by a-wn or blown blast.

The ore or other fine material, brought by a preliminary operation to a suitable con tent in a. heat generating element (sul hur, arsenic, carbon, etc.) may be subjectefte a preparation and/or compression intended to impart to it a suflicient plasticity in order that a subsequent kneading and. threadformmg operation, the ore may be reduced to sufficiently resistant grains nonadherent or little adherent to each other, which ains are afterwards preferably dried and sifted, and. subjected in a uniformly and highly pervious thin layer to a roasting and/or sinterin operation in the manner hereinbefore state By thin layer it is. meant a la er the height of which is smaller than-any o its two other dimensions; I

As sintering blast ap am spiovidea with a grate traversed by b own or drawn blast, use may be advantageousl made of the continuous apparatus calle Dwight Lloyd straight or of the circular Von Schlippenbach apparatus, both of these apparatuses being commonly known in the art.

It is obvious that high furnaces, such as shaft furnaces cannot be used according to the resent invention, because of the small 812 grains.

The fine material to be treated is prefer.- ably moistened with water before bein' compressed and ma also be mixed with a binding material capab e by drying or crystallization, and of producin the hardening of the material without es'troying its perviousness during the roasting operation. The binding material should therefore, when the grains are subjected to the roasting operation, either burn (which is the case with organic binders), or become decomposed at, a low temrature. As a binding material of the latter ind, sulphate of iron may be advantageously used. The sulphate of iron may be replaced the ore.

by an addition of sulphuric acid to the ore,

which acid produces soluble sulphates with It is of course understood that the utilization of sul hate of iron, sulphuric acid or any other binding material when roastin fine ore is known per se and that I do not 0 aim these binding materials as forming my invention. It is in fact ossible to do away with the addition of a inding material by eifecting a preliminary sulphatizing roasting or by leaving the moist material exposed for a certain time to the action of the atmospheric agents.

By way of example, a mode of carrying the invention into effect when ap lied to a dead roastin of blende, is given ereinafter:

The lende subjected to a preliminary roasting until the contents of sulphur are brought to the desired amount (5 to 7%) or brought by mixing to a contents of sulphur or other combustible material correspondin to the same calorific power as 3 to 6% o sulphur in sul hide form, and mixed with 1 to 5% of sulp ate of iron and 5 to 25% of water, is fed into a kneading-threadforming apparatus.

The accompanyin drawin illustrate diagrammatically an by way 0 example, an apparatus which may be advantageously used for carrying the rocess into practice.

' 1 shows t e whole of the apparatus Flg. in a ongitudinal vertical section;

Fig. 2 is a plan view corresponding to Fig. 1; and

Fig. 3 is an elevation on a large scale, of

the kneading-threadforming apparatus.

Having more articular re erence to the drawings, where n like characters of reference will designate corresponding parts throughout, the apparatus may be stated to comprise a tubular mixing body 1 terminated by a conical flaring portion 1' followed by a cylindrical body of larger diameter 2.

Extending longitudinally through the bodies 1 and 2, is a rotatable shaft S carrying at one end a plurality of radially disposed blades 3 adapted to propel the material while mixing and kneading the same. Arranged masses the movement of rotation of the shaft.

. The lower portion of the cylindrical body 2 carries a perforated sieve 2' having perforations measuring from 3 to 5 mm. in diameter, preferably 3 or 4 mm. for the ordinary blends.

The material which arrives kneaded and compressed in the cylindrical portion, is forced by the blades through the sieve and falls in the form of short and rather breakable thin cylinders into the conveyor 7, these cylinders dividing themselves into small pieces of various lengths. The most favourable size for the grains is comprised between 3 and 4 mm. diameter. The length of the grains may vary within larger limits, from 2 to 15 mm. for instance.

The conveyor moves through suitable driving mechanism with a continuous motion, carrying, in the form of a thin and regular layer, the material which is continuously produced by the two kneading-threadforming devices 8 and penetrates inside a tunnel or other drying device 9 kept by a furnace 10 or other source of heat at a suitable temperature. The grains leave dryer in a hardened and more or less completely dried state and fall into a sifting apparatus consisting of two superposed sieves, the upper one 11 having meshes of approximately -10 mm., and the lower one 12 having meshes of approximate: ly 2 mm. A roller 13 disintegrates any eventual conglomerates of grains which may have been formed during the drying operation.

The granulated material, deprived of line dust, falls from the sieve 12 into a storing hop er 14 which distributes it uniformly upon t e grate 15 of the blast apparatus which is displaced underneath it. It should be noted that if the grains, as said above, are subjected to a drying operation, this drying is only necessary up to the desired point for obtaining grains capable of being sifted for eliminating the dust and of being charged onto the grate without the formation of a new also possible to effect a mixed chargingof of a complete dryness; for the blende it will be about 5% of sulphur in sulphide form.

The present process enablesto obtain numerous and important advantages, due essentially to the high and uniform'perviousness of the layer of small-sized grains which are used.

The main advantages are:

1. The desulphurizationis effected verythoroughly and the amount of sulphur which remains in the mass is negligible. It may fall for normal blendes as low as 0.10%.

2. The pressure or depression necessary for the apparatus with forced or drawn blast is reduced, resulting in a saving of motive power and reduction to a large extent, of the air admission which occurs with apparatuses having movable joint-s. By way of example, for a layer of 0.25 m. thickness of grains of 3.5 mm. diameter the depression may vary between 7 and 3 cm. of water. Y

3. The granulated material may be dry and does not require any addition. It has no tendency to the formation of holes through the action of the blast. For the same reasons,

the carrying away of material during the passage of blast is practically nil.

4. The thickness of the layer placed on the blast apparatus may be considerably higher than with nongranulated material whence the costs of ignition are decreased in propor- I tion; a thickness of 0.50 m. should however be considered as being near to the limit which cannot be exceeded in practice owing to the difiiculties arising from an increased pressure or vacuum and to the danger of having the grains crushed by their own weight; moreover the reaction progresses much more rapidly than with non granulated material, whence an increase of the output of the apparatus to very large proportions.

5. The gas which is obtained is for these reasons, comparatively richin sulphur dioxide, SO; (in the case of blende roasting 3 to 5% of sulphur dioxide, SO. can be obtained with a blast apparatus which is well constructed from the point of view of tight-' I 7 joint fit) the gas is on the other hand practically free from water vapour and this is indispensable for certain processes of manufacture of sulphuric acid.

6. Aneven temperature at all points is ob tained without havin' too hot zones where" semi-fusings are pro uced with abundant volatilization of useful metals (zinc, lead, etc.) and cold zones in which the roasting or sintering is incomplete.

7. Lastly, it is Possible to adjust the amount .of heat-producing substances (sulphur inthe case of blendes) and to conduct the blast deliver in such a manner as to obtain a complete roasted product without fusing,scorificat1on or even fritting of the material, in such a -manner that after roasting, th e grains are obtained almost intact in sha e, porous and easily separable from eac other without a troublesome of dust, the material thus obtaine being in'a state which is highly favourable for the subsequent operationsand more particularly for obtaining the reduction of the zinc ores in the zinc oven.

I claim:

1. In a process for the roasting of fine ore material in the form of a comparatively thin layer, the preliminary steps of subjecting the said ore material to a mixing-threadforming operation, whereby threads having all the same small diameter are expressed in a practically vertical direction against a conveyor band which is uniformly moved without shaking, and are bent by the movement of roducti'on the conveyor band so that they break into 5 short pieces having the same small diameter and approximately same length, allowing the said short pieces to dry before disturbing them for the blast roasting operation, as set ameter are expressed in a practically vertical direction against a conveyor band which is uniformly moved without shaking, and are bent by the movement of the conveyor band so that they break into short pieces having the same small diameter and approximately same length, allowing the broken pieces to dry before disturbing them for the blast roasting operation, as set forth.

ADOLPHE DENlS HENRI LEON FASSOTTE. 

